It is know that the mechanical characteristics of the optical fibres on either side of a weld, in particular their breaking elongation are about 20 times smaller than the same characteristics of the original fibre. Due to this fact, when an optical fibre is subjected to traction, the weld zones constitute its weakest parts and when breakage occurs, it occurs at the weld zones.
In the document "A 34-Mbit/s optical field trial system" by E. Adler, H. Haupt and W. Zschunke, read in Geneva at the 4th European Conference on optical communication, held on 12th to 15th Sept., 1978, a proposal was made to reinforce optical fibre weld zones by means of a malleable metal tube of low modulus of elasticity crimped onto the fibre sheaths on either side of the stripped ends. The mechanical properties of a weld zone are thereby improved to some extent but they remain much lower then those of the original fibre.
Also, French patent specification No. 2380559 (equivalent to U.S. Pat. No. 4196965), describes a device for reinforcing the butt weld between two optical fibres whose cladding, of lower refractive index then that of the fibre core is removed in the zone on either side of the butt weld. In said zone, the optical fibres are surrounded by a sleeve consisting of two layers--an inner layer made of fluorinated or silicone resin and whose refractive index is lower than that of the fibre core; and a metal outer layer. The space between the sleeve and the fibre core is optionally filled with a resin of lower refractive index than the fibre core. The sleeve can then have a single metal layer. However, optical cladding made of thermoplastic material which is easy to separate from the fibre core provides a lower quality of fibre from the light transmission point of view and a cladding made of silica or of glass which is difficult to separate from the fibre core. Further, replacing the optical cladding by a sleeve--even a sleeve which has an inner layer made of resin whose refractive index is lower than that of the fibre core--can cause discontinuity in the transmission of the light-radiation at the interface between the optical cladding and the sleeve.
Preferred embodiments of the present invention provide a reinforced connection which imparts to a weld zone mechanical properties (in particular tensile strength and elongation on traction) which are close to those of the original optical fibre, so that said weld zone is not systematically the seat of possible breakage. The reinforced connection is generally easy to prepare and does not give rise to discontinuity in the transmission of light-radiation.